We are studying the functions of docosahexaenoic acid (22:6n3), a dietary essential fatty acid, which is found most abundantly in the lecithins (phosphatidylcholines equals PC) and phosphatidylethanolamines (PE) of animal cell membranes. We have used a diet very low in linolenic acid (18:3n3), the precursor of 22:6n3 to prepare rats in which concentrations of 22:6n3 are very low in phospholipids of various organs. We plan to study the functions of retina, brain, muscle, liver or heart in rats such as these because these tissues were most severely depleted of 22:6n3. We are also studying the formation of lecithins from PE in vitro (cell-free rat liver preparation). Experiments in vivo have suggested that 22:6n3 PE is a favored substrate for the transmethylation reactions that lead to lecithin. The formation of lecithin from PE is the biosynthesis of choline in rats. BIBLIOGRAPHIC REFERENCES: Poovaiah, B. P., J. Tinoco, and R. L. Lyman. Influence of diet on conversion of 14Cl-linolenic acid to docosahexaenoic acid in the rat. Lipids 11: 194-202, 1976. (Reported "in press" last year). Tinoco, J., P. Miljanich, and B. Medwadowski. Depletion of docosahexaenoic acid in retinal lipids of rats fed a linolenic acid-deficient, linoleic acid-containing diet. Biochim. Biophys. Acta, in press, 1977.